Polyolefin production

ABSTRACT

Use of a metallocene compound of general formula (IndH 4 ) 2 R″MQ 2  as a component of a catalyst system in producing polyethylene, wherein each Ind is the same or different and is indenyl or substituted indenyl; R″ is a bridge which comprises a C 1  to C 4  alkylene radical, a dialkyl germanium or silicon or siloxane, alkyl phosphine or amine, which bridge is substituted or unsubstituted, M is a Group IV metal or vanadium and each Q is hydrocarbyl having 1 to 20 carbon atoms or halogen; and the ratio of meso to racemic forms of the metallocene in the catalyst system is at least 1:3. The metallocene may be supported. The ethylene may be polymerized in a reaction medium that is substantially free of any external comonomer, with comonomer being formed in situ. The produced polyethylene may have long chain branching. The produced polyethylene may be atactic.

RELATED APPLICATIONS

This is a continuation application of U.S. patent application Ser. No.10/143,467, which is still pending and which was filed on May 9, 2002,which is also divisional application of U.S. patent application Ser. No.09/299,436, which was filed on Apr. 26, 1999, which claims priority fromEuropean Patent Office (EPO) Application 98107623.5, filed on Apr. 27,1998.

FIELD OF INVENTION

The present invention relates to a process for the preparation ofpolyethylenes and to the use of metallocene compounds as catalystcomponents for use in such a process.

DESCRIPTION

Metallocene-catalysed polymerisation of ethylene is well-known and it iscommon practice to add to the ethylene monomer a comonomer such asbutene. This has the advantage of modifying the properties of thepolyethylene so as to make a range of copolymer products with variousmechanical properties.

Racemic (bis indenyl) ethane zirconium dichloride complexes are known tobe very active polymerisation catalysts for the production ofpolyethylene and low molecular weight isotactic polypropylene incombination with a cocatalyst such as methyl aluminoxane. Theconventional synthetic procedures for producing the racemic complexesalso produce a side product, which is the meso isomer, at a typicallevel of 3-5%.

CA-A-2104036 is directed to the use of various rac/meso mixturesprimarily as catalysts in the production of isotactic polypropylenes.

This patent application also discloses the use of the meso form ofcertain metallocenes to produce atactic polypropylene. In one example,this patent application also discloses the use of a 95:5 rac/mesometallocene in the production of a propylene, ethylene block copolymer.

The present applicants have surprisingly found that the meso form ofcertain metallocenes can be advantageously used as a catalyst in thepolymerisation of ethylene without the need to add exogenous butene tothe reaction mix.

The present invention provides use of a metallocene compound of generalformula Ind₂R″MQ₂ as a component of a catalyst system in the productionof polyethylene, wherein each Ind is the same or different and isindenyl or substituted indenyl; R″ is a bridge which comprises a C₁ toC₄ alkylene radical, a dialkyl germanium or silicon or siloxane, alkylphosphine or amine, which bridge is substituted or unsubstituted, M is aGroup IV metal or vanadium and each Q is hydrocarbyl having 1 to 20carbon atoms or halogen; and the ratio of meso to racemic forms of themetallocene in the catalyst system is at least 1:3.

The present invention further provides a process for the preparation ofpolyethylene, which comprises polymerising ethylene, optionally withhydrogen, in the presence of a catalyst system comprising

(a) a metallocene compound of general formula Ind₂R″MQ₂ as defined inany one of claims 1 to 7;

(b) a cocatalyst which activates the metallocene compound; and

(c) an inert support; wherein the ratio of meso to racemic forms of themetallocene in the catalyst system is at least 1:3.

Each indenyl may bear one or more substituent groups, each of which maybe independently chosen from those of formula XR_(v) in which X ischosen from group IVA, oxygen and nitrogen and each R is the same ordifferent and chosen from hydrogen or hydrocarbyl of from 1 to 20 carbonatoms and v+1 is the valence of X. X is preferably C. If thecyclopentadienyl ring is substituted, its substituent groups must not beso bulky as to affect coordination of the olefin monomer to the metal M.Substituents on the cyclopentadienyl ring preferably have R as hydrogenor CH3. More preferably, at least one and most preferably bothcyclopentadienyl rings are unsubstituted. Each indenyl may be present inreduced form with up to 4 hydrogen substituents, such as in a 4, 5, 6, 7tetrahydroindenyl.

In a particularly preferred embodiment, both indenyls are unsubstituted.

R″ is preferably an ethylene bridge which is substituted orunsubstituted.

The metal M is preferably zirconium, hafnium or titanium, mostpreferably zirconium. Each Q is the same or different and may be ahydrocarbyl or hydrocarboxy radical having 1-20 carbon atoms or ahalogen. Suitable hydrocarbyls include aryl, alkyl, alkenyl, alkylarylor aryl alkyl. Each Q is preferably halogen. Ethylene bis(1-indenyl)zirconium dichloride is a particularly preferred bis indenyl compound ofthe present invention.

The metallocene catalyst component used in the present invention can beprepared by any known method. A preferred preparation method isdescribed in J. Org. Chem. 288, 63-67 (1985).

The cocatalyst which activates the metallocene catalyst component can beany cocatalyst known for this purpose such as an aluminium-containingcocatalyst or a boron-containing cocatalyst. The aluminium-containingcocatalyst may comprise an alumoxane, an alkyl aluminium and/or a Lewisacid.

The alumoxanes used in the process of the present invention are wellknown and preferably comprise oligomeric linear and/or cyclic alkylalumoxanes represented by the formula:

for oligomeric, linear alumoxanes and

for oligomeric, cyclic alumoxane, wherein n is 1-40, preferably 10-20, mis 3-40, preferably 3-20 and R is a C₁-C₈ alkyl group and preferablymethyl.

Generally, in the preparation of alumoxanes from, for example, aluminiumtrimethyl and water, a mixture of linear and cyclic compounds isobtained.

Suitable boron-containing cocatalysts may comprise a triphenylcarbeniumboronate such as tetrakis-pentafluorophenyl-borato-triphenylcarbenium asdescribed in EP-A-0427696, or those of the general formula [L′-H]+[B Ar₁Ar₂ X₃ X₄]- as described in EP-A-0277004 (page 6, line 30 to page 7,line 7).

Preferably, the same catalyst system is used in both steps (i) and (ii)of the process. The catalyst system may be employed in a solutionpolymerisation process, which is homogeneous, or a slurry process, whichis heterogeneous. In a solution process, typical solvents includehydrocarbons with 4 to 7 carbon atoms such as heptane, toluene orcyclohexane. In a slurry process it is necessary to immobilise thecatalyst system on an inert support, particularly a porous solid supportsuch as talc, inorganic oxides and resinous support materials such aspolyolefin. Preferably, the support material is an inorganic oxide inits finally divided form.

Suitable inorganic oxide materials which are desirably employed inaccordance with this invention include Group 2a, 3a, 4a or 4b metaloxides such as silica, alumina and mixtures thereof. Other inorganicoxides that may be employed either alone or in combination with thesilica, or alumina are magnesia, titania, zirconia, and the like. Othersuitable support materials, however, can be employed, for example,finely divided functionalized polyolefins such as finely dividedpolyethylene.

Preferably, the support is a silica having a surface area comprisedbetween 200 and 900 m2/g and a pore volume comprised between 0.5 and 4ml/g.

The amount of alumoxane and metallocenes usefully employed in thepreparation of the solid support catalyst can vary over a wide range.

Preferably the aluminium to transition metal mole ratio is in the rangebetween 1:1 and 100:1, preferably in the range 5:1 and 50:1.

The order of addition of the metallocenes and alumoxane to the supportmaterial can vary. In accordance with a preferred embodiment of thepresent invention alumoxane dissolved in a suitable inert hydrocarbonsolvent is added to the support material slurried in the same or othersuitable hydrocarbon liquid and thereafter a mixture of the metallocenecatalyst component is added to the slurry.

Preferred solvents include mineral oils and the various hydrocarbonswhich are liquid at reaction temperature and which do not react with theindividual ingredients. Illustrative examples of the useful solventsinclude the alkanes such as pentane, iso-pentane, hexane, heptane,octane and nonane; cycloalkanes such as cyclopentane and cyclohexane;and aromatics such as benzene, toluene, ethylbenzene and diethylbenzene.

Preferably the support material is slurried in toluene and themetallocene and alumoxane are dissolved in toluene prior to addition tothe support material.

Preferably no comonomer is added to the ethyl and hydrogen during thepolymerisation. This avoids the need to remove unwanted excess butene orother comonomer.

The polyethylene formed in accordance with the present inventionpreferably has long chain branching with a shear ratio of preferably atleast 20, more preferably at least 30. These properties confer upon thepolyethylene good processability characteristics and a smooth glossysurface.

Without wishing to be bound by any theory it is postulated thatcomonomer is not required in the polymerisation because butene is formedin situ at the active site of the metallocene catalyst, probably byethylene dimersation. Butene found in situ would react very quickly witha growing polymer chain because no diffusion barrier would be present.

The invention will now be described in further detail, by way of exampleonly, with reference to the following Examples and the accompanyingdrawings, in which:

FIG. 1 shows a 13C NMR spectrum of a polyethylene made in accordancewith the present invention; and

FIG. 2 shows a 13C NMR spectrum of a further polyethylene made inaccordance with the present invention.

EXAMPLE 1

Catalyst Preparation

(a) Synthesis of the Stereoisomers

High yield rapid synthesis of the rac/meso(bisindenyl)ethanezirconiumdichloride: The freshly prepared diaromatized bisindenylethane ligand issuspended in pentane and reacted with an equimolar suspension of ZrCl₄in pentane. The slurry is stirred for three Hours and filtered. Yellowsolid is extracted with methylene chloride to separate the LiCl.According to NMR of the crude product a more or less quantitative yieldfor the rac/meso mixture is obtained according to this method.

(b) Isolation of the Pure Stereoisomers

Solubility test showed that the meso isomer has about three times highersolubility in toluene. In this way the meso can be concentrated intoluene and completely separated from the racemic byproduct.

The support used in a silica having a total pore volume of 4.217 ml/gand a surface area of 322 m²/g. This silica is further prepared bydrying in high vacuum on a schlenk line for three hours to remove thephysically absorbed water. 5 g of this silica are suspended in 50 ml oftoluene and placed in a round bottom flask equipped with magneticstirrer, nitrogen inlet and dropping funnel.

An amount of 0.31 g of the metallocene is reacted with 25 ml ofmethylalumoxane (MAO 30 wt % in toluene) at a temperature of 25° C.during 10 minutes to give a solution mixture of the correspondingmetallocenium cation and the anionic methylalumoxane oligomer.

Then the resulting solution comprising the metallocenium cation and theanionic methylalumoxane oligomer is added to the support under anitrogen atmosphere via the dropping funnel which is replacedimmediately after with a reflux condenser. The mixture is heated to 110°C. for 90 minutes. Then the reaction mixture is cooled down to roomtemperature, filtered under nitrogen and washed with toluene.

The catalyst obtained is then washed with pentane and dried under a mildvacuum.

EXAMPLE 2

Polymerisation Procedure and Results

Ethylene was polymerised under the conditions described in Table 1 in a41 batch reactor at a temperature of 80° C. for a residence time of 60mins. Supported catalyst was precontacted with triisobutylaluminium(TBAC) and introduced into the reactor in which 21 of isobutene wereused as diluent. The metallocene was present at 100 mg and thecocatalyst at 390 ppm. TABLE 1 Hydrogen Comonomer Yield Hourly Prod M12HLMI Density Bulk Density Run (wt %-NL) (wt %) (g) (g/g · hr) (g/10′)(g/10′) SR (g/cc) (g/cc) A 0 0.00 183 1830 0.14 8.47 60 0.9438 0.28 B 01.22 250 2500 0.65 27.06 42 0.9385 0.37 C 0 2.44 346 3460 1.23 40.31 330.9380 0.27 D 0 3.66 390 3900 2.47 74.42 30 0.9550 0.29 E 0 4.88 2702700 4.98 152.40 31 0.9521 0.30 F 0.25 0.00 166 1660 1.94 65.94 340.9530 0.36 G 0.25 1.22 345 3450 0.78 28.57 37 0.9623 0.35 H 0.25 2.44255 2550 4.75 157.60 33 0.9429 0.31 I 0 0.00 338 3380 0.06 3.75 600.9574 0.24 J 0 2.44 695 6950 0.14 8.63 62 0.9366 0.35 K 0.25 2.44 6766760 0.54 21.76 40 0.9421 0.39 L 0.25 3.66 720 7200 0.58 23.37 40 0.94070.34 M 0.25 4.88 922 9220 0.72 25.38 35 0.9394 0.32 Hydrogen ComonomerMn Mw Run (wt %-NL) (wt %) (kDa) (kDa) Mz (kDa) Mp (kDa) D D′ A 0 0.0028.376 134.8 451.0 94 4.7 3.4 B 0 1.22 26.388 101.6 334.6 53 3.9 3.3 C 02.44 23.139 94.6 354.7 45 4.1 3.8 D 0 3.66 22.848 75.0 215.0 42 3.3 2.9E 0 4.88 19.658 64.6 202.0 32 3.3 3.1 F 0.25 0.00 15.320 88.8 421.4 435.8 4.7 G 0.25 1.22 25.920 105.7 366.3 56 4.1 3.5 H 0.25 2.44 17.52873.6 262.8 37 4.2 3.6 I 0 0.00 37.464 155.2 528.2 65 4.1 3.4 J 0 2.4434.036 122.0 375.5 60 3.6 3.1 K 0.25 2.44 25.657 115.1 423.9 56 4.5 3.7L 0.25 3.66 25.164 110.3 402.4 52 4.4 3.6 M 0.25 4.88 27.177 99.5 335.149 3.7 3.4Runs A to H, Ethylene 6 wt %;Runs I to M, Ethylene 10 wt %

Table 1 represents the polymerisation conditions, results and polymeranalysis for the meso stereoisomer. The polymerization activityincreases with increasing comonomer content in the feed regardless ifhydrogen is present or not. A maximum activity of 4000 g PE/g cat for 6%ethylene and 10000 g PE/g cat for 10% ethylene concentration has beenreached with different hexene concentration at this stage. The densitybehaviour is also interesting with respect to the hexene concentration;it does not decrease gradually with increasing hexene concentration.This behaviour is related to the in situ butene formation (cf. 13C NMR).For a monomodal polymer formed with a single site catalyst the SRs ofthe polymers are very large (35-60). The most important practicalconsequence of large SR, related to long chain branching (cf. 13C NMR),is the fact that the specimens that have been obtained from the meltindexer show no signs of melt fracture (good processibility) and thecorresponding plaques are of very smooth and glossy surfaces.

13C NMR Analysis of PE Homo- and Copolymers

Table 2 sets out the results of 13C NMR analysis of the polyethylenesproduced under the conditions of some of the runs detailed in Table 1.The averages of three NMR analyses are shown. Representative spectrafrom runs A and C are shown in FIGS. 1 and 2 respectively. The spectraindicate a very good comonomer incorporation capability and theformation of long chain branching. In addition to the hexene (Butanebranching) substantial amounts of butene (ethyl branching) are observedin the backbone of the polymers. Most important is the signal pattern ofthe spectrum in FIG. 1 of the polymer produced in the absence of anytype of external comonomer. It shows up to 1 wt % Butene and confirmsthe in situ formation of butene via dimerization of ethylene. Since noother signals related to other comonomers is observed it can beconcluded that the dimerization mechanism is very specific. Theformation of long chain branching and comomoner is part of the uniqueproperties of this catalytic system. TABLE 2 Hydrogen Comonomer (wt%-NL) (wt %) % C4m % C4w % C6m % C6w A 0 0 0.44 0.88 0 0 B 0 1.22 0.380.75 0.44 1.31 C 0 2.44 0.27 0.53 0.75 2.21 D 0 3.66 0.26 0.51 1.14 3.32E 0 4.88 0.30 0.58 1.72 4.97 G 0.25 1.22 0.28 0.57 0.17 0.52 I 0 0 0.370.74 0 0 J 0 2.44 0.33 0.65 0.50 1.48 L 0.25 3.66 0.24 0.48 0.49 1.45% Cm = molar % compared with ethylene% Cw = weight % compared with ethylene

1. A process for preparing a polyethylene copolymer, which comprises:polymerizing ethylene, without using an exogenous comonomer, with acatalyst system comprising: a metallocene compound of general formulaInd₂R″MQ₂ having a mole ratio of meso to racemic forms of themetallocene of at least 1:3, wherein each Ind is the same or different,and is indenyl or substituted indenyl, R″ is a bridge that issubstituted or unsubstituted and comprises a C₁ to C₄ alkylene radical,a dialkyl germanium or silicon or siloxane, alkyl phosphine or amine, Mis a Group IV metal or vanadium, each Q is a hydrocarbyl having 1 to 20carbon atoms or a halogen, said catalyst being further comprised of aninert support; and wherein a cocatalyst is used to activate themetallocene compound.
 2. The process according to claim 1, wherein thepolyethylene formed thereby has a shear ratio of at least
 20. 3. Theprocess according to claim 1, wherein the cocatalyst comprisestriisobutylaluminium (TBAC), and wherein said catalyst is precontactedwith TBAC.
 4. The process according to claim 1, wherein hydrogen isadded during polymerization.
 5. The process according to claim 1,wherein butane comonomer is formed in situ by dimerization of butane andwherein polymerization activity increases with increasing comonomercontent.
 6. The process according to claim 1, wherein the polyethyleneformed thereby has short chain branching arising from C₄ incorporationinto the backbone of the polyethylene.
 7. The process according to claim1, wherein the cyclopentadienyl ring of at least one of the indenyls isunsubstituted without regard to the bridge R″.
 8. A catalyst accordingto claim 1, wherein the cocatalyst comprises an aluminum-containingcocatalyst or a boron-containing cocatalyst.
 9. A catalyst according toclaim 1, wherein the cocatalyst comprises an aluminum-containingcocatalyst comprised of an alumoxane, an alkyl aluminum and/or a Lewisacid.
 10. A long chain branched polyethylene copolymer formed by aprocess comprising: copolymerizing ethylene in a reaction medium whichcomprises a solution or slurry with a catalyst system comprising: ametallocene compound of general formula Ind₂R″MQ₂ having a mole ratio ofmeso to racemic forms of the metallocene of at least 1:3, wherein eachInd is the same or different and is indenyl or substituted indenyl, R″is a bridge that is substituted or unsubstituted and comprises a C₁ toC₄ alkylene radical, a dialkyl germanium or silicon or siloxane, alkylphosphine or amine, M is a Group IV metal or vanadium, each Q is ahydrocarbyl having 1 to 20 carbon atoms or a halogen, said catalystbeing further comprised of an inert support; using a cocatalyst whichactivates the metallocene compound; and wherein said ethylene ispolymerized without use of an exogenous comonomer.
 11. The processaccording to claim 10, wherein butane comonomer is formed in situ bydimerization of butane and wherein polymerization activity increaseswith increasing comonomer content.
 12. A catalyst according to claim 10,wherein R″ is an ethylene bridge.
 13. A catalyst according to claim 10,wherein both indenyls are unsubstituted without regard to the bridge R″.14. A catalyst according to claim 10, wherein M is Zr.
 15. A catalystaccording to claim 10, wherein the Q is a halogen.
 16. A catalystaccording to claim 10, wherein the bis indenyl compound is ethylene. 17.A catalyst according to claim 10, wherein the cocatalyst which activatesthe metallocene compound comprises an aluminum-containing cocatalyst ora boron-containing cocatalyst.
 18. A catalyst according to claim 10,wherein the cocatalyst comprises an aluminum-containing cocatalystcomprising an alumoxane, an alkyl aluminum and/or a Lewis acid.
 19. Aprocess for polymerizing ethylene comprising: forming a supportedmetallocene catalyst by adding an alumoxane dissolved in an inerthydrocarbon solvent to a slurry of a inert particulate support, whereinsaid particulate support material comprises silica particles having asurface area within the range of 200-900 m²/g and a pore volume withinthe range of 0.5-4.0 ml/g; adding a metallocene compound of the generalformula Ind₂R″MQ₂ having a mole ratio of meso to racemic forms of themetallocene of at least 1:3, wherein each Ind is the same or differentand is an indenyl or substituted indenyl, R″ is a bridge that issubstituted or unsubstituted and comprises a C₁ to C₄ alkylene radical,a dialkyl germanium or silicon or siloxane, alkyl phosphine or amine, Mis a Group IV metal or vanadium, each Q is hydrocarbyl having 1 to 20carbon atoms or halogen; contacting said supported catalyst withethylene to polymerize ethylene to produce an ethylene copolymer; andrecovering said ethylene copolymer.
 20. The process of claim 19, whereinhydrogen is added to said reaction medium.
 21. The process of claim 19,wherein ethylene is polymerized in a reaction medium that issubstantially free of any external comonomer.
 22. The process of claim19, wherein atactic polyethylene is produced.